豫西崤山东部中河岩体锆石U-Pb年龄、地球化学和Lu-Hf同位素特征

Zircon U-Pb age,geochemistry and Lu-Hf isotopic characteristics of Zhonghe intrusion in eastern Xiaoshan,Henan Province

中河花岗斑岩体位于河南省崤山东部,该岩体是最近发现的中河大型银铅锌矿床的成矿母岩。选取2件花岗斑岩样品进行LA-ICP-MS锆石U-Pb定年,获得2件样品的^(206)Pb/^(238)U年龄加权平均值分别为(129±0.7)Ma(MSWD=0.78)和(131±1.5)Ma(MSWD=1.70),表明中河岩体形成于早白垩世。岩石地球化学特征显示,中河岩体具有高的w(SiO_2)和w(K_2O)、低的w(Na_2O),其A/CNK比值为1.03~1.63,Mg#值介于25~50,总体上属于过铝质-强过铝质的高钾钙碱性系列。岩石具有低的w(Yb),中等-弱的铕负异常,稀土元素配分曲线为轻稀土元素富集型,轻稀土元素分馏相对强烈,但重稀土元素分馏不明显。中河岩体有相对低的w(Sr)和w(Y),且富集大离子亲石元素Rb、Ba、U、K和轻稀土元素,亏损高场强元素Nb、Ta、P、Zr、Hf、Ti和重稀土元素。中河岩体锆石εHf(t)值为-34.4^-23.2,平均为-26.9,Hf同位素二阶段模式年龄介于2485~3182 Ma,平均为2714 Ma。岩石地球化学特征及Hf同位素组成表明中河岩体的岩浆源区主要为新太古代地壳物质,并有少量的中太古代地壳物质,中-新太古代增生的具有弧岩浆特征的地壳物质部分熔融形成了早白垩世的中河岩体。

The granitic Zhonghe intrusion,located in eastern Xiaoshan of Henan Province,has a close genetic relation with the large-sized Zhonghe Ag-Pb-Zn deposit recently discovered in Luoning County.Two granite porphyry samples from the Zhonghe intrusion were selected for LA-ICP-MS zircon U-Pb dating,which yielded weighted mean 206Pb/238U ages of(129±0.7)Ma(MSWD=0.78)and(131±1.5)Ma(MSWD=1.70),respectively,indicating that the Zhonghe intrusion formed during Early Cretaceous.The petrogeochemical data show that Zhonghe intrusion has high w(SiO2)and w(K2O)content and low w(Na2O)content,its A/CNK values vary from 1.03 to 1.63,and its Mg#values range from 25 to 50.The Zhonghe intrusion generally belongs to a high-K calk-alkaline series.The granitic rocks reveal low w(Yb)content and intermediately-weakly negative Eu anomalies,and their rare earth element(REE)distribution patterns are characterized by enrichment of light REEs(LREEs),with strong LREEs fractionation but weak heavy REEs(HREEs)fractionation.The Zhonghe intrusion has low Sr and Y content,and is characterized by enrichment of Rb,Ba,U,K and LREEs and depletion of Nb,Ta,P,Zr,Hf,Ti and HREEs.The granite porphyry has low zirconεHf(t)values of-34.4^-23.2 with an average value of-26.9,and old Hf two-stage model ages of 2485~3182 Ma with an average age of 2714 Ma.The petrogeochemical characteristics and Hf isotopic compositions indicate that magmatic source of the Zhonghe intrusion was dominated by a Neoarchean crust with the addition of a small amount of Mesoarchean crust,and that the Zhonghe intrusion most likely originated from a partial melting of the Meao-Neoarchean crust,which formed in a Meao-Neoarchean island arc environment.